I have gone Kookoo

[Russ White]

There it is sitting on my desk, a prototype Joshua Tree attenuator just waiting for action. I can't help but feel sad at the waste. So lonely, just waiting for action. This little attenuator needs a home!!!

You can read about the Joshua Tree here:

http://www.diyaudio.com/forums/showt...119#post848119

So what did I do?

Well I already had one in my XBOSOZ setup for balanced operation, and I really didn't need a preamp, but what the heck, I built one anyway.

Part of me said, “Hey Russ, you know that XBOSOZ you have right now so rocks, but hey its not the easiest thing to build, maybe some people want rocking good preamplification without the stress. I talk to myself a lot. I continued ... “Hmmmmm, maybe something similar in function but much simpler”. Then I had a few beers and went to sleep, then the next morning I dug out another project (its a DAC) that needed an IV stage. Well what I had sketched out was two independent buffers. Hmmm that jogged my memory back to that solitary attenuator.... What if... what if.... Maybe... Why not!!!

So here is what I did, I built 2 simple opamp based stereo buffer/preamp(you can give them gain or not its up to you) circuits on one PCB with an on board power supply which just happens to be the exact same size as the Joshua Tree PCBs and will fit right above or below. You feed it a signal it amplifies it (10db in the case of my prototype) in the first stage, then it passes the output to the input of the JT(Joshua Tree) which in turn passes its attenuated output to the next “stage” which amplifies the signal another 10db. This give me a complete preamp with no pot in the signal path and 128 step of attenuation from about -60db to +20db, and 100K(adjustable by resistor choice) input impedance and next to nothing for output impedance.... AWESOME!!!

So with that mental picture in my head I drove to work, and during a slow hour or two drew the attached circuit. Now keep in mind this is a very simple version, but it works very well. I plan on a much more refined version very soon. Here are some PICs to whet your appetite for now. The prototype sounds fabulous. I used OPA2228 for the first tests, but I will try other opamps as well. It is hard to turn the thing off long enough to swap them though.

In keeping with my bird brained theme for this kind of stuff I called it the “Kookoo”. And yes many say it is a reflection of my personality.

[Russ White]

Here is how the finished application looks:

[Panelhead]

Russ,
Do you ever sleep? This looks great. Any plans on adding this to the product line after the JT is released?

George

[Russ White]

Originally posted by Panelhead
Russ,
Do you ever sleep? This looks great. Any plans on adding this to the product line after the JT is released?

George

Hi George,

Thanks, I am glad you like it.

First, the current orders for JTs should be out the door. Brian did an awesome job of getting the kits together. That man is the best friend a guy could have.

And yes, the idea is that this would be a natural fit to our kit line, but as always it is the DIY project that comes first and all information and schematics and such are provided freely. If you want to build one yourself independantly that is great! Speakng of schematics I will post these too, I just need to clean them up a bit here.

Cheers!
Russ

[jleaman]

Russ,

I think you need some sleep

I emailed a whyle back about a idea for your volume pot.

[Russ White]

I will be creating an AD815 version (thanks to Carlos, and a whole slew of others for all the good work on that) for an output stage. The constant output impedance of the JT into the AD815 should be a nice situation allowing for a simple DC nulling circuit such as Carlos used with no need for a servo. Then driving a hard load like low inpedance headphones will be cake! I also may play with some other high current devices.


Any recommendations?

[neutron7]

could you make it take single op amps as an option or is the board too small?

[Russ White]

Originally posted by neutron7
could you make it take single op amps as an option or is the board too small?

I think I actually could especially if I went SMD. That actually was my first inclination, but I wanted to do the first protoype as easily (or quickly) as possible.

Cheers!
Russ

[jleaman]

The more i play with toys and fix other equipment that is smd the more i like it. I used to hate it but now i like it. Russ i think you should make it smd after.

[pinkmouse]

That's enough pettyness, can we stick to the design now.